1. Field of the Invention
This invention relates to collapsible cores. More specifically, this invention relates to collapsible cores useful in the molding of threaded plastic closures. Still more specifically, this invention relates to collapsible cores useful for molding threaded closures in which the threads are in the form of a plurality of thread segments. It is also useful for other undercut products.
2. Description of the Prior Art
In the prior art there are a number of patents showing collapsible cores used in making threaded closures. By means of such collapsible cores it is not necessary once a threaded cap, for instance, is molded to "unscrew" it from its core; instead the core is collapsed and the threaded closure is simply stripped off the collapsed core.
Some examples in the prior art include, for instance, U.S. Pat. No. 3,618,170, E. W. Owens, granted Nov. 9, 1971, which shows a collapsible core presenting a pair of core portions which are held in proper molding relation by an actuator, the sides of which have non-threaded segments. Once the closure is molded, the actuator is withdrawn and the portions of the core are permitted to collapse inward so that the closure may be readily stripped.
Another example of a collapsible core is disclosed in U.S. Pat. No. 4,019,711 to J. Altenhof et al which issued Apr. 26, 1977. In this patent a plurality of thread-molding segments ride in grooves on the core. These segments have threaded sides. Once the closure is molded, the segments will move longitudinally of the core on a incline so that when the segments are fully extended, their diameter is reduced and the closure may be stripped to provide a closure having segmented threads.
A still further example of a collapsible core is shown in the U.S. Pat. No. 4,130,264 to Schroer which issued Dec. 19, 1978. In this patent there are a plurality of segments about the periphery of the core. The segments, once the molding is complete, move on tracks at different inclinations so that the core, when collapsed, may be easily stripped. The product in this instance is a closure having threads on its inside all the way around.